1. Field of the Invention
This invention relates to balloon valvuloplasty and, more particularly, to the method and apparatus for passing an expandable catheter into a valve of the heart and expanding the catheter to effect changes in the valve.
2. Description of the Prior Art
Stenosis, or narrowing of a valve's orifice, is a serious medical condition, generally the result of fusion and immobility of the valve leaflets. Stenosis may be congenital or may be acquired, as for example to sequel to rheumatic fever. In he past, traditional treatments of valvular stenosis have been surgical, employing open heart methods and techniques to either mobilize the existing valve leaflets or, more commonly, to insert a prosthetic valve of a mechanical nature or one derived from animal tissue.
These treatments are less than ideal. Surgery carries risk to life and large expense. Also, persons implanted with a mechanical valve must remain on anticoagulant medication for the remainder of their lifetime. Further, a significant disadvantage to insertion of mechanical valves in the heart is the problem or reliability of the mechanical device. Mechanical valves are subject to failure by fatigue or fracture of the constituent materials. The biologic valves (e.g. porcine or bovine material) are subject to degeneration of the tissues making up the valve.
Because of the shortcomings in the prior mechanical valves and the other difficulties inherent in the open heart methods developed, a relatively new technique of palliative nature has been developed, known as balloon valvuloplasty. In this procedure, a balloon mounted on a plastic tubular catheter is inserted into a blood vessel, passed into the heart and positioned with its deflated balloon member lying within the stenotic valve that is to be treated. The balloon is then inflated quickly with radio-opaque fluid several atmospheres' pressure. Fluoroscopy visualizes the expanding balloon and enables a judgement regarding the degree with which the valve leaflets have been rendered more mobile.
Balloon valvuloplasty has largely been performed with catheters carrying a single, cylindrical balloon of circular cross-section. In a significant proportion of such valvuloplasties, particularly involving the mitral valve whose leaflets present a somewhat elliptical or "fish-mouth" orifice, successful valvuloplasty has required the passage of two such balloon catheters across the mitral orifice side by side, and simultaneous inflation of both balloons. This requirement is made necessary because of the shape of the orifice ideally desired after treatment. Specifically, the mitral valve has only two leaflets and it is therefore necessary to be able to mobilize or "crack" the valve up to the portions of the valve commissures at the periphery of the valve ring, rather than only in the center of the valve.
Needless to say, simultaneous inflation of separate balloon catheters is a reatively difficult procedure requiring coordination of two separate catheters and is therefore more time consuming and riskier because of the difficulty in the simultaneous positioning of the catheters without mutual interference.
Attempts have been made to avoid the difficulties produced in the side-by-side or simultaneous operation of valvuloplasty balloons. An example of this is a "trifoil balloon having three balloons of equal size and shape. The balloons are disposed around the central catheter tube at intervals of 120.degree.. The three balloons are commonly connected to the catheter lumen such that all three balloons inflate simultaneously. While suited for stenotic aortic pulmonic valves which are composed of three mobile semi-lunar leaflets, the "trifoil" balloon arrangement is not suitable for the mitral valve or for a congenitally bicuspid aortic valve. Even for use with stenotic aortic or pulmonic valves, the "trifoil" balloon cannot enter the narrower confines of the valve commissures without significant distortion of the balloon, which is unlikely.
Many patents have issued dealing with different types of expandable catheters. Examples of such patents are those to:
______________________________________ Schultz 4,141,364 Hattler et al. 4,406,656 Van Tassel et al. 4,531,943 Fugua 4,601,713 ______________________________________
These patents, however, do not resolve the problems presently discussed.
Schultz, 4,141,364, discloses an expandable endotracheal or urethral tube which contains a number of sections which can be inflated. However, this device is not suited for, nor is it designed to deal with the problems of the specific shaped involved with the valvuloplasty procedure.
Hattler et al., 4,406,656, discloses multi-lumen catheters where fluid flowing in certain lumens causes these lumens to expand, and the absence of fluid-flow in the lumens causes the lumens to contract. As discussed at length in columns 1 and 2 of this patent, a number of prior-art patents relating to multi-lumen catheters are available. However, this patent does not deal with expandable catheters adapted for use in the valvuloplasty field.
Van Tassel et al., 4,531,943, teaches the use of a soft deformable member attached to the distal tip of a catheter. The deformable tip may comprise an inflatable balloon element attached to the distal end of the tip of the catheter. By selectively inflating the balloon tip, the effective area of the tip can be increased to reduce the overall force per unit area at a point of contract between the tip of the catheter and the blood vessel. However, this patent does not deal with the problem of the specialized shapes necessary for valvuloplasty.
Fugua, 4,601,713, deals with catheters applied to urology. the patent indicates that the so-called "Foley" catheter includes a tube with an inflatable cup or balloon at the distal end of the catheter so as to hold the catheter in place. Specifically, the balloon is inflated to retain the catheter in the bladder. However, the patent does not at all deal with catheters that would be suitable for use in valvuloplasty.